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How many amps are you comfortable with?
#1
I have a 160p7s pack and I get a bit concerned when my inverters are pulling 40 amps. It's only .035 amps per cells but it still registers as a high amount with me, even though I build them to theoretically handle a lot more. How many amps per cell are you happy to charge/discharge?
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#2
Check your math...  40 amps / 160 cells = 0.25 amps per cell

It's more a questions of the actual pack design and how the bus bars are configured...  and also if the packs layout allows for an even distribution of resistance so the power is consumed evenly across the pack.

If the pack is build well, 40 amps may be a breeze... is not, you would start seeing issues.  

The higher the load, the more it matters.  Combine this with a Hodge podge of mixed cells with varying internal resistance and I can almost guarantee you not all cells are contributing evenly at your 0.25 amp per cell target.

Its fun to poke around with an amp meter of measure the mV delta under load at each branch to get an idea.
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#3
(07-10-2020, 09:03 PM)Cell-King Wrote: ...............How many amps per cell are you happy to charge/discharge?........

I have a 14s80p pack and I have a similar setup as you . Difference is I have 2 GTIL2 1000 with just CTs.
My max is 900W each so 1800W which translates at 48V (kinda my minimum I will let my cells go) 38.2A
Call it 40A for easy math. That's 0.5A per cell at max.  I'm good with that as all my cells are tested very thorough and have great IR.

Will you be running your GTs at 100% all the time?
I mean my nigh time when I have a full charge is tops 10A 0.125A per cell.
If your build has the proper backbone ie Buss bar and cabling no problem. With my build I am comfortable with 80A if it ever gets that high but doubtful.

Red Line is Battery amps  plus and minus. Green line is both GTIL combined. The others are charge controllers 2 and 3.
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#4
btw, it's 7s160p Wink As I'm sure you only have 1 bms, not 7

Most cells of the laptop variety, are designed to be able to handle .5A (500mA) [generally this is listed as .20C for a 2500mAh cell or similar]. Use the Cell Database to get the actual limits of the cells used. Obviously, you want to go by the "lowest rated" cell to determine what your pack limits are.

As mentioned, the buss bar is a major factor, as well. If it's too small to handle the amps, it's gonna get hot and waste energy.
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#5
I'm running dual AIMS 12,000w inverters from a 48v battery bank.   That's a continuous 500a @ 48v range.   AIMS can do 3x for 20secs - so in theory that's 1,500a for a few seconds.   However, each inverter has a 250a circuit breaker and the overall battery bank has a 400a ABB shunt-trip.   400a = 660ma/cell (OK for battery design), Batrium is up to the BMS task, and equipment is all ETL/UL. 

I'm comfortable with 400a @ 48v Smile      

I do agree - it's a step by step process where good technique - e.g. metal boxes, proper wiring/circuit-breakers to isolate sections, conduit, + and - at opposite ends of the cells (cannot be easily shorted), check-lists of what to turn off to work on things so I don't forget...   all are necessary (for me) to have that confidence.
completelycharged and Korishan like this post
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#6
Thanks for the advice guys, I always assumed the amp draw per cell be the total amp divided by the total number of cells 1120/40, not 160/40. Big difference!
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